This relates to testing devices with antennas, and more particularly, to testing multi-antenna devices.
Electronic devices such as handheld electronic devices, portable electronic devices, and computers often have wireless communication capabilities. Electronic devices with wireless communication capabilities typically include antennas. Antennas transmit and receive radio frequency (RF) signals.
It may be desirable to incorporate more than one antenna in a single electronic device. Electronic devices with more than one antenna may sometimes be referred to as multi-antenna devices. Multi-antenna devices may exhibit improved performance over single-antenna devices. The performance improvement provided by multi-antenna devices may depend on factors such as multipath propagation, spatial correlation of the wireless signals, delay/frequency spread of the wireless signals, etc. It may be desirable to optimize multi-antenna devices while taking into account the various factors that affect device performance.
In order to optimize the design of multi-antenna devices, it may be useful to test a wireless communications system in which data is sent back and forth between a first device and a second device. The first and second devices may each have more than one antenna. Wireless signals that travel back and forth between the first and second devices may travel through a channel whose properties are affected by the presence of obstacles, reflective materials, and other environmental factors.
For example, imagine a scenario in which a cellular telephone is communicating wirelessly with a base station. The wireless communications channel in this type of scenario will be influenced by physical variations in terrain between the cellular telephone and the cell tower such as the presence of buildings, moving cars, mountains, regions of water, etc.
Efforts have been made to simulate communications systems using software. In software simulations, the behavior of communications devices and the wireless channel are handled using software abstractions. Software simulations are not necessarily accurate models of the actual characteristics of a channel and the interactions between the communicating devices and the channel.
To address the shortcomings of software simulations, efforts have also been made to simulate a communications system using channel emulator hardware. In a typical test arrangement, a first device may have a first RF front end disconnected from the antenna of the first device. The first RF front end may be connected to an input of a channel emulator. A second device may have a second RF front end that is disconnected from the antenna of the second device. The second RF front end may be connected to an output of the channel emulator. The channel emulator attempts to recreate the characteristics of a real-life channel (e.g., multipath gain, multipath delay, etc.). Because the channel emulator makes simplifying assumptions about the behavior of a typical channel, the channel emulator will not be able to effectively model how the antennas behave within the device housing, how polarization and gain effects impact antenna performance, or how devices with multiple antennas operate.
Moreover, conventional test arrangements that are used for testing MIMO systems do not accurately emulate uplink channel fading and uplink path loss. The conventional test systems use uplink path loss values that are different than the path loss values experienced by radio-frequency signals in realistic wireless networks. The uplink signal path of conventional test systems typically remains unperturbed by any form of fading and sees low levels of attenuation. Testing multi-antenna devices in this way may not be capable of accurately characterizing uplink performance.
It would therefore be desirable to be able to provide improved ways to test wireless communications performance for devices with antennas.